Field of the Invention
The present invention relates to an ESD (Electrostatic Discharge) protection technology, particularly to a touch control device with enhanced ESD protection effect.
Description of the Related Art
With advance of display panel technology and popularization of consumer electronic products, more and more touch panels or touchscreens are used as the operating interfaces of electronic products, from the military devices to hi-tech electronic appliances. A touch control device, such as a touch panel or a touchscreen, can detect touches. In the field of touch control, a touch is normally referred to a contact of a finger (or a hand) with the sensing region of a touch control device. However, the sensing region of a touch control device can also sense the contact of other objects, such as a touch control stylus. Touch control devices have many applications, such as operating interfaces of portable electronic devices and tablet computers.
The touch control device has two significant advantages: the user can directly interact with the information displayed on the screen; and no intermediate device, such as the mouse or the keyboard, is required between the user and the electronic product. Touch control devices not only are used in larger computers and mechanical apparatuses but also are applied to smaller electronic products, such as personal digital assistants (PDA), GPS (Global Positioning System) navigation devices, mobile phones, video garners, etc. Because of simple operation and diversified functions, touch control devices are more and more popularized in daily life.
According to the operation principles, the touch control devices may be classified into four types: the resistive type, the capacitive type, the optical type and the ultrasonic type. The resistive touch control device comprises upper and lower ITO (Indium Tin Oxide) conductive layers, spacers and electrodes, wherein two pieces of ITO glass are used as the substrates; ITO films are respectively disposed on the substrates; spacers are interposed between two substrates to prevent from conduction between two substrates; silver electrodes are printed on the edges of the substrates for supplying voltage. The capacitive touch control device comprises a glass insulator coated with a transparent conductor (such as sensing electrodes made of ITO), and a touch sensor IC (Integrated Circuit) electrically connected with sensing electrodes and measuring capacitive variation in the electrodes, wherein the capacitive variation is used as a sensation signal, and the touch sensor IC receives the sensation signal and points out the contact position. The optical touch control device operates according to the blocked light beam and comprises glass substrates, infrared sources and infrared receivers, wherein many infrared sources and infrared receivers are distributed on the device and arranged to form an array; while an infrared light beam is blocked, some infrared receivers cannot receive infrared light; the contact position is worked out according to positions of the infrared receivers unable to receive infrared light. The ultrasonic touch control device comprises transmission transducers, reception transducers, reflector boards and a controller, wherein transmission transducers, reflector boards and reception transducers are arranged on each of the X coordinate and the Y coordinate of a piece of glass.
When the user operates the touch control device, the electrostatic charges carried by the finger are likely to conduct to the screen of the touch control device and induce ESD. The withstanding voltage of the circuits inside the touch control device is normally only tens of volts. ESD may substantially affect or damage the circuits and electronic elements inside the touch control device. For example, ESD may cause screen defects, melt metal conduction lines, vary the resistance of elements, damage or puncture oxide layers, cause malfunctions of the circuits and controllers centering around the processor. Any of the abovementioned events would significantly decrease the service life of the touch control device and affect the reliability of signal transmission.
Refer to FIG. 1 a plan view schematically showing a touch control device using the conventional ESD protection technology. In the conventional touch control device 10 shown in FIG. 1, an ESD protection ring 16 is disposed on the periphery of a sensing region 12 and a plurality of signal lines 14. Once a user touches the touch control device 10, the sensing region 12 generates a sensation signal, and the signal lines 12 transmit the sensation signal to the control unit of the touch control device 10, wherein the signal lines and the control unit transmit signals reciprocally. Electrostatic charges are likely to form during signal transmission and likely to appear in the signal lines 14 and the sensing circuit module. The ESD protection ring 16 is to drain off electrostatic charges, whereby to protect the electronic elements in the sensing circuit module and maintain the correctness and integrality of signal transmission.
Although the conventional technology has installed an ESD protection ring on the periphery of the signal lines and electronic elements of the touch control device, the ESD protection ring cannot drain off all electrostatic charges but can only prevent from a half of electrostatic discharges. Therefore, the conventional touch control device still risks electrostatic discharges, which may shorten the service life of the device and lower reliability of signal transmission.
In order to overcome the conventional problems, the present invention proposes a touch control device with enhanced ESD protection effect, which additionally installs an ESD shield between the signal lines and the ESD protection ring to achieve a full ESD protection effect.